Conventionally, LIN (local interconnect network) has been widely used as a short range communication technology. The LIN is a technology for achieving bidirectional communication between a master station and a slave station through a same communication path of communication. This technology has been developed to distributedly control multiple control targets mounted in a vehicle. The LIN is characterized in that, in data transmission based on pulse width, to reduce communication errors attributed to a communication clock difference between communication stations, data for baud rate adjustment is transmitted from the master station to the slave station to bring a baud rate of the slave station and a baud rate of the master station into agreement, based on that baud rate data. According to this characteristic, although highly reliable distributed control can be achieved, transmission of data for baud rate adjustment unreasonably extends communication time. Particularly in a distributed control system, the LIN is not so preferable because of possible reduction in control response.
Conventionally, as a technology for achieving bidirectional communication between a master station and a slave station through a same communication path of communication, JP-8-265308A proposes that data represented by the duty ratio of pulses is transmitted from a master station to a slave station, while data represented by pulse amplitude is transmitted from the slave station to the master station. Thus, the bidirectional data transmission is achieved every communication cycle period. According to this characteristic, since communication time can be reduced. As a result, if this technology is used in a distributed control system, high control response is expected to be obtained.
In the technology disclosed in JP-8-265308A, the duty ratio of pulses can be easily changed by using an electric circuit for LIN. However, to change the amplitude of pulses, it is necessary to provide the slave station with a special electric circuit for adjusting and outputting the amplitude of transmission pulses, and provide the master station with a special electric circuit for detecting the amplitude of reception pulses. As a result, costs will increase.